View source for Tiny-BCU

= Idea =

* BCU without ready-to-use KNX Transceiver like OnSemi, Siemens or Elmos
* Small µC that reads/writes the bits to KNX bus and
* "emulates" a reduced KNX TPUART BCU protocol

= Benefits =

* No dependency to onsemi & co: OnSemi had several times delivery difficulties; Elmos can not be ordered when you're private person, Siemens is not cheap
* better handling wrt. bus powered supply
* easier to build, due to no QFN package
* Parts typically all available at german distributeros/electronic shops
* possibly different and thus easier communication protocol (I2C?)
* possibly more cpu cycles for the sketch due to caching on TinyBCU controller?!

= Cons = 

* not that tiny as MicroBCU due to more parts on PCB
* possibly not significant cheaper than traditional BCU

= Requirements =

* Transceiver-Part: something to read/write the bits physically from/to KNX bus; simple analog circuit for extracting/inserting the bits from/to bus.
* Controller-Part: something that can interpret the bits from transceiver-part and make it BCU-style readable + write the bits of a telegram to the transceiver-part
* Supply-Part: voltage and current from bus: at least 3.3V and 5V with about &gt;=50mA, without creating interferrences on the BUS

= Transceiver-Part =

See: https://github.com/selfbus/hardware-incubation/tree/master/module/UPModule

= Supply-Part =

See: https://github.com/selfbus/hardware-incubation/tree/master/module/UPModule
For instance one can also use the "Polulu" step-down modules to create 3.3V and 5V from up to 40V input. The are multiple candidates available, f.i. from TI

= Controller-Part =

Something like the Attiny85.

Features:

* Interrupt-Pin: https://hoeser-medien.de/2015/04/attiny85-interrupt-basierend-auf-pinchange-interrupt-library/
* UART via softserial
* ultra low power
* small and also in DIP available --> easy to solder. Even with socket one can remove the chip to program it.

Open questions: How to debug? Maybe develop with Arduino UNO and then port to attiny?

SW: See: https://github.com/selfbus/software-arm-lib/tree/master/sblib/inc/sblib/eib